The present application claims priority of Chinese patent application Serial No. 200710119871.5, filed Aug. 2, 2007 and Chinese patent application Serial No. 200810081325.1, filed Feb. 25, 2008, the content of which is hereby incorporated by reference in its entirety.
1. Field of Invention
The present invention relates to the field of radiographic imaging technology, and in particular to a scan radiographic imaging method used in a system for radiographic examination of large-sized objects.
2. Description of Prior Art
With the help of the penetrating capability of high-energy X-rays, radiographic imaging technology can look into the inner structure of an object in a non-contact manner so as to obtain a transmission image of the object. For the examination of large objects in the prior art, the operation principle of scanning radiographic imaging is that X-rays are emitted by a radiation source, penetrate through an object to be detected, are received by a detector and then converted into electric signals to be inputted into an image acquisition system, which in turn inputs the image signals into a computer monitor for displaying the detected image. In general, a transmission image by radiographic imaging is actually the projection of every object penetrated by the beam of X-rays and contains no information about spacial depth. Therefore, a scan image will be one formed by superimposing the projection of each of the multiple objects along a scanning beam if all the objects are exactly located in the incident direction of X-rays. This is adverse to the examination of an object hidden behind the others. In order to overcome the above problem, in the field of radiographic imaging there has been proposed a relatively mature technology for object reconstruction, which utilizes computerized tomography scanning technique. Unfortunately, this technique has drawbacks of complex structure, high cost, inability to carry out a quick examination on large objects and low passing-through ratio. Further, the material of the examined object cannot be identified.
In contrast, the processing technique of binocular steroscopic radiographic transmission image is a radiographic imaging method that can separate, from an image, each object at a different depth in a detection space to remove any unwanted obstacle. This technique can be used to peel off some overlapping objects in the transmission image so that the overlaid objects appear more obvious. However, the material property of an object cannot be identified. On the other hand, the identification technique for multi-energy radiographic transmission image can identify the material property, such as organic, mixture, metal, etc., by using the fact that certain object has a varying attenuation capability with respect to different levels of energy. Unfortunately, this technique can identify only the material property of the object that dominates the attenuation absorption when the objects overlap on each other. The property of an object cannot be identified with this technique if the object absorbs only a trivial part of the overall attenuation.